A workpiece is often supported in an oven by a grate formed of a plurality of grate elements each constituted as a tube through which a heat-exchange fluid is circulated to prevent the grate elements themselves from being excessively heated and damaged.
Although normally the entire support tube of such a grate element is at substantially the same temperature due to the fluid traversing it, it is nonetheless subject to considerable temperature changes causing a large degree of thermal expansion. As these support tubes are normally supported between their ends on upright posts the result is that these posts are themselves subject to considerable bending stress as the support tubes they carry expand and contract.
It has been suggested to form a sliding joint between the upper end of each post and the respective support tube. Thus as the support tubes expand and contract they can slide relative to their posts, with only modest force transmission between the tubes and the posts. Such an arrangement is only a partial solution, in that with time the sliding joint between the post upper end the support tube offers greater and greater resistance to sliding so that, once again, the posts are subject to considerable bending stress. Furthermore such a system is completely unusable in an arrangement such as described in now abandoned U.S. Pat. application 785,681 filed 7 Apr. 1977 by Heinz WESTERHOFF where the posts themselves are also traversed by the cooling fluid, as there is no practical way to pass the fluid across the sliding joint.
In another arrangement which allows cooling of the posts the lower end of the posts are provided with roller shoes. Thus as the tube expands and contracts the roller shoes at the lower ends of the posts can move in the direction of expansion and contraction. This arrangement has the disadvantage, once again, that any resistance to displacement of the roller shoe at the bottom of the post is converted into a bending stress in the respective post. As such an arrangement is often used in a metallurgical oven or the like, fouling of the rollers is an inevitability, so that the arrangement must be serviced frequently.